1. Field of the Invention
This invention relates to a container holding an adsorbent, the container being made of a laminate having a polytetrafluoroethylene (hereinafter abbreviated as PTFE) porous film and to the laminate useful to make the container.
The present application is based on Japanese Patent Application No. Hei. 11-14173, which is incorporated herein by reference.
2. Description of the Related Art
In recent years a hard disk drive of a computer has been made more and more compact and increasingly gained in capacity, and improvement on reliability of the hard disk drive has been desired accordingly. Causes which may impair the reliability of a hard disk drive include damage of the disk drive head by suspended particles and contamination of the disk with vapor of organic matter. It has therefore been proposed to place a porous container containing an adsorbent in a hard disk drive thereby to remove the contaminants.
Since an adsorbent increases the adsorption efficiency with its surface area, it is used in the form of particles. A particulate adsorbent unavoidably contains very small particles and also develops fine dust due to friction among the particles. If such small particles and dust scatter outside the container, the adsorbent itself becomes a source of contaminants. Therefore it is desired that the porous container be made of such a material that does not let out fine particles or dust of the adsorbent.
Nonwoven fabric or mesh is generally used as a porous material for enclosing an adsorbent, but it is too coarse to block passage of fine particles. Hence a PTFE porous film has been proposed as a material of a porous container for a particulate adsorbent.
For example, Japanese Patent Publication No. Hei. 4-501229 discloses a porous container made of PTFE porous tubing having an average pore size of 0.1 to 1 μm. The container disclosed is an extruded tube with sealed ends. The extruded tube has a film thickness of about 250 to 1250 μm.
A container equipped with an ultra high molecular weight polyolefin porous film is also known, although the container is for putting a deliquescent adsorbent therein. For example, Japanese Patent Publication No. Hei. 9-276643 discloses a dehumidifier having on the upper part thereof an ultra high molecular polyethylene porous film. According to the disclosure, the ultra high molecular weight polyethylene porous film is used as a material that is permeable to moisture but impermeable to water. Having such a water-impermeable film, the container, even if it falls, does not leak the water generated from the deliquescent adsorbent. The ultra high molecular weight polyethylene porous film used here has a thickness of about 0.8 to 1.5 mm.
Compared with nonwoven fabric and the like, a PTFE porous film attains high efficiency in collecting fine particles. However, the PTFE porous tube as taught in Japanese Patent Publication No. Hei. 4-501229 is not easy to shape to fit the inside of a hard disk drive having an ever decreasing size so that the place inside the drive where such a container can be set may be limited. Further, the PTFE porous tube requires some film thickness to secure strength enough to hold an adsorbent, which restricts permeability, making it difficult to obtain sufficient adsorption performance.